Closed loop Multiple Input Multiple Output (MIMO) systems are efficient to enhance the performance in a fading environment, and can offer higher data rates than single-antenna systems.
In a general closed loop MIMO system, a receiver estimates channel state information and feeds back the estimated channel state information to a transmitter over a feedback link. It is advantageous to use the perfect channel state information in the closed loop MIMO system. However, the capacity of the feedback link is very limited.
In the general closed loop MIMO system, a precoding scheme is used when the feedback link from the receiver to the transmitter is present. In particular, the performance of the quantized precoding scheme is determined by design and complexity of a codebook.
The codebook design has been researched for Institute of Electrical and Electronics Engineers (IEEE) 802.16m system and Long Term Evolution (LTE) system. Codebooks of various optimization schemes and types have been suggested, whereas a codebook to adopt is not yet determined and a codebook design for better performance is under examination.
In this respect, what is needed is a codebook with good performance and a feedback method using the same.